Method and system for compositing images to produce a cropped image

ABSTRACT

A method for producing a cropped digital image, includes the steps of: providing a plurality of partially overlapping source digital images; providing a cropping aspect ratio L:H, the cropping aspect ratio being the ratio of the length to the height of the cropped digital image; providing a cropping criterion, the cropping criterion being a criterion for the size and location of the cropped digital image; combining the source digital images to form a composite digital image; selecting the cropping region of the composite digital image according to the cropping criterion, said cropping region being a rectangular region having aspect ratio L:H, and having size and location determined by the cropping criterion; and, cropping the composite digital image to the cropping region to form a cropped digital image.

FIELD OF THE INVENTION

[0001] The invention relates generally to the field of digital imageprocessing, and in particular to a technique for compositing multipleimages into a large field of view image, said image being cropped to aselected aspect ratio.

BACKGROUND OF THE INVENTION

[0002] Conventional systems for generating images comprising a largefield of view of a scene from a plurality of images generally have twosteps: (1) an image capture step, where the plurality of images of ascene are captured with overlapping pixel regions; and (2) an imagecombining step, where the captured images are digitally processed andblended to form a composite digital image.

[0003] In some of these systems, images are captured about a common rearnodal point. For example, in U.S. Ser. No. 09/224,547, filed Dec. 31,1998 by May et. al., overlapping images are captured by a digital camerathat rotates on a tripod, thus ensuring that each image is captured withthe same rear nodal point lying on the axis of rotation of the tripod.

[0004] In other systems, the capture constraint is weakened so that theimages can be captured from substantially similar viewpoints. Oneexample of a weakly-constrained system is the image mosaic constructionsystem described in U.S. Pat. No. 6,097,854 by Szeliski et al., issuedAug. 1, 2000; also described in Shum et al., “Systems and ExperimentPaper: Construction of Panoramic Image Mosaics with Global and LocalAlignment,” IJCV 36(2), pp. 101-130, 2000. Another example is the“stitch assist” mode in the Canon PowerShot series of digital cameras(see http://www.powershot.com/powershot2/a20_a10/press.html; U.S. Pat.No. 6,243,103 issued Jun. 5, 2001 to Takiguchi et al.; and U.S. Pat. No.5,138,460 issued Aug. 11, 1992 to Egawa.

[0005] In some systems, the capture constraint is removed altogether,and the images are captured at a variety of different locations. Forexample, the view morphing technique described in Seitz and Dyer, “ViewMorphing,” SIGGRAPH '96, in Computer Graphics, pp. 21-30, 1996, iscapable of generating a composite image from two images of an objectcaptured from different locations.

[0006] The digital processing required in the image combining stepdepends on the camera locations of the captured images. When the rearnodal point is exactly the same, the image combining step comprisesthree stages: (1) a warping stage, where the images are geometricallywarped onto a cylinder, sphere, or any geometric surface suitable forviewing; (2) an image alignment stage, where the warped images arealigned by a process such as phase correlation (Kuglin, et al., “ThePhase Correlation Image Alignment Method,” Proc. 1975 InternationalConference on Cybernetics and Society, 1975, pp. 163-165), or crosscorrelation (textbook: Gonzalez, et al., Digital Image Processing,Addison-Wesley, 1992); and (3) a blending stage, where the alignedwarped images are blended together to form the composite image. Theblending stage can use a simple feathering technique that uses aweighted average of the images in the overlap regions, and it canutilize a linear exposure transform (as described in U.S. Ser. No.______, filed Nov. 5, 2001 by Cahill et al., our docket no. 83516/THC)to align the exposure values of overlapping images. In addition, aradial exposure transform (as described in U.S. Ser. No. ______, filedDec. 17, 201 by Cahill et al., our docket 83512/THC) can be used in theblending stage to compensate for light falloff.

[0007] In weakly-constrained systems, the image combining step generallycomprises two stages: (1) an image alignment stage, where the images arelocally and/or globally aligned according to some model (such as atranslational, rotational, affine, or projective model); and (2) ablending stage, where the aligned images are blended together to form atexture map or composite image. The blending stage typicallyincorporates a de-ghosting technique that locally warps images tominimize “ghost” images, or areas in the overlapping regions whereobjects are slightly misaligned due to motion parallax. The localwarping used by the de-ghosting technique can also be incorporated inthe model of the image alignment stage. For an example of imagecombining with such a system, see the aforementioned Shum and Szeliskireferences.

[0008] In systems where the capture constraint is removed altogether,the image combining step first requires that the epipolar geometry ofthe captured images be estimated (for a description of estimatingepipolar geometry, see Zhang, et al., “A Robust Technique for MatchingTwo Uncalibrated Images Through the Recovery of the Unknown EpipolarGeometry,” INRIA Report No. 2273, May 1994, pp. 1-38). Once the epipolargeometry has been estimated, the images are projected to simulatecapture onto parallel image planes. The projected images are thenmorphed by a standard image morphing procedure (see Beier et al.,“Feature-Based Image Metamorphosis,” SIGGRAPH '92 Computer Graphics,Vol. 26, No. 2, July 1992, pp. 35-42), and the morphed image isreprojected to a chosen view point to form the composite image. Anexample of such a system is described in the aforementioned Seitz andDyer reference.

[0009] In all of the prior art methods and systems for generating largefield of view images, the composite image is provided as output. In someinstances, however, it might be necessary to provide a composite imagethat has been cropped and/or zoomed to a selected aspect ratio and size.For example, consider a digital photofinishing system that printshardcopies of images that have been digitized from film after beingcaptured by an Advanced Photo System (APS) camera. APS cameras providethe photographer the choice of receiving prints in three differentformats: HDTV (H), Classic (C), or Panoramic (P). The Classic formatcorresponds to a 3:2 aspect ratio, the HDTV format to a 16:9 aspectratio, and the Panoramic format to a 3:1 aspect ratio. If thephotographer captures a sequence of images with an APS camera and usesone of the known techniques to generate a composite image, the compositeimage will likely not have an aspect ratio corresponding to the H, C, orP formats. Since one of these three formats would be required in thedigital photofinishing system, the photographer must manually interveneand crop the composite image to the appropriate aspect ratio forprinting.

[0010] There is a need therefore for an improved method that willcombine images into a composite image; the method being capable ofautomatically cropping the composite image to a desired aspect ratio.

SUMMARY OF THE INVENTION

[0011] The need is met according to the present invention by providing amethod for producing a cropped digital image that includes the steps of:providing a plurality of partially overlapping source digital images;providing a cropping aspect ratio L:H, the cropping aspect ratio beingthe ratio of the length to the height of the cropped digital image;providing a cropping criterion, the cropping criterion being a criterionfor the size and location of the cropped digital image; combining thesource digital images to form a composite digital image; selecting thecropping region of the composite digital image according to the croppingcriterion, said cropping region being a rectangular region having aspectratio L:H, and having size and location determined by the croppingcriterion; and, cropping the composite digital image to the croppingregion to form a cropped digital image.

Advantages

[0012] The present invention has the advantage of automaticallyproducing a cropped digital image in a system for compositing aplurality of source digital images. This eliminates the need for theuser to crop and/or resize the composite digital image.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a block diagram illustrating a digital image processingsystem suitable for practicing the present invention;

[0014]FIG. 2 illustrates in block diagram form, the method of forming acropped digital image from at least two source digital images;

[0015]FIG. 3 illustrates the preferred cropping criterion;

[0016]FIG. 4 illustrates an alternative cropping criterion;

[0017]FIG. 5 illustrates a further alternative cropping criterion;

[0018]FIG. 6 illustrates in block diagram form, an embodiment of thestep of selecting a cropping region according to the preferred croppingcriterion;

[0019]FIG. 7 illustrates in block diagram form, a further embodiment ofthe step of providing source digital images;

[0020]FIGS. 8A and 8B illustrate in block diagram form, furtherembodiments of the step of providing source digital images;

[0021]FIG. 9 illustrates in block diagram form, a further embodiment ofthe step of combining source digital images;

[0022]FIG. 10 is a diagram useful in describing the step of combiningthe adjusted source digital images;

[0023]FIG. 11 illustrates in block diagram form, a further embodiment ofthe step of blending warped digital images;

[0024]FIGS. 12A and 12B are diagrams useful in describing the aspectratio of an image; and

[0025]FIGS. 13A and 13B illustrate a source digital image filecontaining image data and meta-data.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described as implemented in aprogrammed digital computer. It will be understood that a person ofordinary skill in the art of digital image processing and softwareprogramming will be able to program a computer to practice the inventionfrom the description given below. The present invention may be embodiedin a computer program product having a computer readable storage mediumsuch as a magnetic or optical storage medium bearing machine readablecomputer code. Alternatively, it will be understood that the presentinvention may be implemented in hardware or firmware.

[0027] Referring first to FIG. 1, a digital image processing systemuseful for practicing the present invention is shown. The systemgenerally designated 10, includes a digital image processing computer 12connected to a network 14. The digital image processing computer 12 canbe, for example, a Sun Sparcstation, and the network 14 can be, forexample, a local area network with sufficient capacity to handle largedigital images. The system includes an image capture device 15, such asa high resolution digital camera, or a conventional film camera and afilm digitizer, for supplying digital images to network 14. A digitalimage store 16, such as a magnetic or optical multi-disk memory,connected to network 14 is provided for storing the digital images to beprocessed by computer 12 according to the present invention. The system10 also includes one or more display devices, such as a high resolutioncolor monitor 18, or hard copy output printer 20 such as a thermal orinkjet printer. An operator input, such as a keyboard and track ball 21,may be provided on the system.

[0028] Referring next to FIG. 2, at least two source digital images areprovided 200 in the method of the present invention. The source digitalimages can be provided by a variety of means; for example, they can becaptured from a digital camera, extracted from frames of a videosequence, scanned from photographic film or hardcopy output, orgenerated by any other means. A cropping aspect ratio L:H is alsoprovided 202. The cropping aspect ratio is the ratio of the length(distance of the horizontal edge) to the height (distance of thevertical edge) of the desired cropped digital image. For example, in adigital photofinishing system that prints hardcopies of images that havebeen digitized from film after being captured by an Advanced PhotoSystem (APS) camera, the cropping aspect ratio is constrained to beeither 16:9, 3:2, or 3:1, corresponding to HDTV, Classic, and Panoramicformats, respectively.

[0029] A cropping criterion is also provided 204. The cropping criterionspecifies the size and location of the cropped digital image. In thepreferred embodiment, the cropping criterion states that the croppeddigital image be the composite digital image region having the largestarea out of the set of all regions having aspect ratio L:H. In analternative embodiment, the cropping criterion is that the croppeddigital image be the composite digital image region having the largestarea out of the set of all regions having aspect ratio L:H and havingcenters at the centroid of the composite digital image. In yet anotheralternative embodiment, the cropping criterion is that the croppeddigital image be the composite digital image region having the largestarea out of the set of all regions having aspect ratio L:H and havingcenters at the centroid of the main subject of the composite digitalimage.

[0030] The source digital images are then combined 206 by a scheme knownin the art for combining images captured from the same nodal point,similar nodal points, or different nodal points, to form a compositedigital image. In step 208, a cropping region is selected, the croppingregion being a composite digital image region having aspect ratio L:Hprovided in step 202, selected according to the cropping criterionprovided in step 204. Once the cropping region has been selected 208,the composite digital image is cropped 210 to the cropping region,yielding the cropped digital image 212.

[0031] In one embodiment, the current invention further comprises thestep of resizing 214 the cropped digital image. For example, considerthe digital photofinishing system that prints hardcopies of images thathave been digitized from film at an aspect ratio of 3:2, and requiresthe spatial resolution of images to be 6000 pixels by 4000 pixels. Iffour digital images are provided to the method of FIG. 2, each digitalimage having a spatial resolution of 6000 pixels by 4000 pixels, thecropped digital image may have spatial resolution 9000 pixels by 6000pixels. In order to render a hardcopy print of the cropped digital imagethrough the digital photofinishing system, the cropped digital image isresized to have spatial resolution 6000 pixels by 4000 pixels. Theresizing step can be performed by any technique known in the art; forexample, bilinear interpolation, bicubic interpolation, splineinterpolation, or any of a variety of other image resizing techniques(see textbook: A. K. Jain, “Fundamentals of Digital Image Processing,”Prentice Hall, 1989, Chapter 4, pp. 80-131, for a discourse on imagesampling and resizing).

[0032] In another embodiment, the current invention further comprisesthe step of transforming 216 the pixel values of the cropped digitalimage to an output device compatible color space. The output devicecompatible color space can be chosen for any of a variety of outputscenarios; for example, video display, photographic print, inkjet print,or any other output device.

[0033] Referring next to FIG. 3, the preferred cropping criterion isillustrated. The source digital images 300 overlap in overlapping pixelregions 302. In step 206, the source digital images are combined to formthe composite digital image 304. The cropping region 306 is thenselected in step 208 according to the cropping criterion 204. In thepreferred embodiment, the cropping region 306 has the largest area ofall composite digital image regions having aspect ratio L:H. In someinstances, there can be more than one distinct composite digital imageregion having aspect ratio L:H and having maximum area, yieldingmultiple candidate regions for the cropping regions. In such instances,there may be a small (e.g. less than 10) or very large (e.g. more than10) set of candidate regions. Furthermore, in instances where there isan very large set of candidate regions, the centroids of the candidateregions may form one or more path segments.

[0034] If only one candidate region exists, it is chosen as the croppingregion. If a small number of candidate regions exist, the croppingregion is chosen randomly from the small set of candidate regions. If avery large number of candidate regions exist, and the centroids of thosecandidate regions form a single path segment, the cropping region ischosen to be the candidate region whose center corresponds to the centerof the path segment. If a very large number of candidate regions exist,and the centroids of those candidate regions form more than one distinctpath segment, one path segment is chosen at random, and the croppingregion is chosen to be the candidate region whose center corresponds tothe center of that path segment.

[0035] Referring next to FIG. 4, another embodiment of the croppingcriterion is illustrated. The cropping region 400 of the compositedigital image 402 is the region having the largest area of all compositedigital image regions having aspect ratio L:H, and having a center atthe centroid 404 of the composite digital image 402.

[0036] Referring next to FIG. 5, another embodiment of the croppingcriterion is illustrated. The cropping region 500 of the compositedigital image 502 is the region having the largest area of all compositedigital image regions having aspect ratio L:H, and having a center at amain subject 504 of the composite digital image 502. The main subject504 of the composite digital image 502 can be indicated manually, ordetermined automatically by techniques known in the art; see U.S. Pat.No. 6,282,317 issued Aug. 28, 2001 to Luo et al., for an example ofautomatic main subject detection, which is incorporated herein byreference.

[0037] Referring next to FIG. 6, a block diagram of the method forchoosing a candidate region according to the preferred croppingcriterion 204 is shown. First, any composite digital image region havingaspect ratio L:H and maximum area is identified 600 as a candidateregion. A query 602 is made as to whether there is a single candidateregion. An affirmative response means that the candidate region ischosen 604 as the cropping region. A negative response leads to a query606 as to whether there are a small number of candidate regions. Anaffirmative response means that one candidate region 608 is chosen asthe cropping region. The candidate region can be chosen arbitrarily, forexample, by listing all of the candidate regions, and then by choosingthe first candidate region in the list. A negative response leads to aquery 610 as to whether there is a single path containing centers ofcandidate regions. An affirmative response leads to the choice 612 ofthe candidate region whose center corresponds to the midpoint of thepath as the cropping region. A negative response leads to the choice 614of one of the paths. The path can be chosen arbitrarily for example, bylisting all of the paths, and then by choosing the first path in thelist. The candidate region whose center corresponds to the midpoint ofthe chosen path is chosen 616 as the cropping region.

[0038] Referring next to FIG. 7, the step 200 of providing at least twosource digital images further comprises the step 704 of applying ametric transform 702 to a source digital image 700 to yield atransformed source digital image 706. A metric transform refers to atransformation that is applied to the pixel values of a source digitalimage, the transformation yielding transformed pixel values that arelinearly or logarithmically related to scene intensity values. Ininstances where metric transforms are independent of the particularcontent of the scene, they are referred to as scene independenttransforms.

[0039] In one example of such an embodiment, a source digital image 700was provided from a digital camera, and contains pixel values in thesRGB color space (see Stokes et al., “A Standard Default Color Space forthe Internet—sRGB”, http://www.color.org/sRGB.html, pp. 1-12). A metrictransform 702 is used to convert the pixel values into nonlinearlyencoded Extended Reference Input Medium Metric (ERIMM) (PIMA standard#7466, found on the World Wide Web at(http://www.pima.net/standards/it10/IT10_POW.htm), so that the pixelvalues are logarithmically related to scene intensity values.

[0040] The metric transform is applied to rendered digital images, i.e.digital images that have been processed to produce a pleasing resultwhen viewed on an output device such as a CRT monitor or a reflectionprint. For digital images encoded in the sRGB metric transform is agamma compensation lookup table that is applied to the source digitalimage 700 first. The formula for the gamma compensation lookup table isas follows. For each code value cv, ranging from 0 to 255, an exposurevalue ev is calculated based on the logic:

if (cv<=<10.015) ev=cv/(255*12.92)

otherwise

ev=(cv/255)+0.055)/1.055)^(0.45)

[0041] Once the pixel values are modified with the gamma compensationlookup table, a color matrix transform is applied to compensate for thedifferences between the sRGB color primaries and the ERIMM metric colorprimaries. The nine elements of the color matrix τ are given by:

[0042] 0.5229 0.3467 0.1301

[0043] 0.0892 0.8627 0.0482

[0044] 0.0177 0.1094 0.8727

[0045] The color matrix is applied to the red, green, blue pixel data as

R′=τ ₁₁ R+τ ₁₂ G+τ ₁₃ B

G′=τ ₂₁ R+τ ₂₂ G+τ ₂₃ B

B′=τ ₃₁ R+τ ₃ G+τ ₃₃ B

[0046] where the R, G, B terms represent the red, green, blue pixelvalues to be processed by the color matrix and the R′, G′, B′ termsrepresent the transformed red, green, blue pixel values. The R′, G′, andB′ pixel values are then converted to a log domain representation thuscompleting the metric transformation from sRGB to ERIMM.

[0047] Referring next to FIG. 8A, the step 200 of providing at least twosource digital images further comprises the step 804 of modifying thepixel values of at least one of the source digital images 800 by alinear exposure transform so that the pixel values in the overlapregions of overlapping source digital images are similar. A linearexposure transform refers to a transformation that is applied to thepixel values of a source digital image, the transformation being linearwith respect to the scene intensity values at each pixel. Examples oflinear exposure transforms can be found in the aforementioned Cahill,Gindele, Gallagher, and Spaulding reference.

[0048] Referring next to FIG. 8B, the step 200 of providing at least twosource digital images further comprises the step 802 of modifying thepixel values of at least one of the source digital images 800 by aradial exposure transform so that any light falloff present in thesource digital images is compensated. A radial exposure transform refersto a transformation that is applied to the pixel values of a sourcedigital image, the transformation being a function of the distance fromthe pixel to the center of the image. Examples of radial exposuretransforms can be found in the aforementioned Cahill and Gindelereference.

[0049] Referring next to FIG. 9, a more detailed description of the step206 of combining source digital images is described. The source digitalimages are geometrically warped 900 to compensate for distortion due toperspective projection. In a physical sense, this distortion would notexist if the sensor were not planar, but rather spherical (with theradius of the sphere depending on the focal length of the lens). Thewarped source digital images are then aligned 902 to identify theoverlapping regions. The alignment procedure is performed using any ofthe aforementioned techniques, such as phase correlation or crosscorrelation. Once the source digital images have been aligned, they areblended 904 in the overlapping regions.

[0050] Referring next to FIG. 10, the blending step 904 furthercomprises a feathering scheme, weighted averages, or some othertechnique known in the art, to form a composite digital image. In oneembodiment, a pixel 1002 in the overlap region 1004 is assigned a valuebased on a weighted average of the pixel values from both source digitalimages 1000; the weights are based on its relative distances 1006 to theedges of the source digital images 1000.

[0051] Referring next to FIG. 11, a further embodiment of the step 904of blending warped digital images is described. The warped digitalimages are projected 1100 to simulate capture on parallel image planes.This is done by estimating the fundamental matrix relating the twoimages. The fundamental matrix, described in the aforementioned Zhang,Deriche, Faugeras, and Luong reference, contains all of the informationpertinent to the geometrical relationship between two cameras. Once thewarped digital images have been projected 1100 to simulate capture onparallel image planes, they are morphed 1102 using a standard imagemorphing procedure, such as the procedure described in theaforementioned Beier and Neely reference, producing a morphed digitalimage. A set of viewing parameters at which to view the morphed digitalimage is chosen 1104, and the morphed digital image is then reprojected1106 to the chosen viewing parameters, producing the composite image.The blending step 904 described in this embodiment is the well knownview morphing procedure, described in the aforementioned Seitz and Dyerreference.

[0052] Referring next to FIGS. 12A and 12B, the aspect ratio of an image1200 is defined as the ratio of the length 1202 of the image to itsheight 1204. When the width 1204 of the image is greater than its length1202, as depicted in FIG. 12A, the aspect ratio is less than one, and isreferred to as a portrait aspect ratio. When the width 1204 of the imageis less than its length 1202, as depicted in FIG. 12B, the aspect ratiois greater than one, and is referred to as a landscape aspect ratio.Advanced Photo System (APS) cameras provide the choice of threedifferent aspect ratios: HDTV (H), a 16:9 aspect ratio, Classic (C), a3:2 aspect ratio, or Panoramic (P), a 3:1 aspect ratio. These aspectratios are all landscape aspect ratios, but the APS camera can berotated to capture images with the corresponding portrait aspect ratios9:16, 2:3, and 1:3.

[0053] Referring next to FIGS. 13A and 13B, at least one of the sourcedigital image files 1300 may contain meta-data 1304 in addition to theimage data 1302. Such meta-data can include the cropping aspect ratio1306, or any information pertinent to the pedigree of the source digitalimage.

[0054] The invention has been described in detail with particularreference to certain preferred embodiments thereof, but it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention.

Parts List

[0055] PARTS LIST 10 digital image processing system 12 digital imageprocessing computer 14 network 15 image capture device 16 digital imagestore 18 high resolution color monitor 20 hard copy output printer 21keyboard and trackball 200 provide source digital images step 202provide cropping aspect ratio step 204 provide cropping criterion step206 combine source digital images step 208 select cropping region step210 crop composite digital image step 212 cropped digital image 214resize cropped digital image step 216 transform pixel values step 300source digital images 302 overlapping pixel regions 304 compositedigital image 306 cropping region 400 cropping region 402 compositedigital image 404 centroid of composite digital image 500 croppingregion 502 composite digital image 504 main subject of composite digitalimage 600 identify candidate regions step 602 single candidate regionquery 604 cropping region chosen 606 finite number of candidate regionsquery 608 cropping region chosen 610 single path of candidate regioncenters query 612 cropping region chosen 614 choose first path step 616cropping region chosen 700 source digital image 702 metric transform 704apply metric transform step 706 transformed source digital image 800source digital images 802 modify with linear exposure transform step 804modify with radial exposure transform step 900 warp source digitalimages step 902 align warped digital images step 904 blend warpeddigital images step 1000 source digital images 1002 pixel 1004overlapping pixel region 1006 distances to image edges 1100 projectwarped digital images step 1102 morph projected digital images step 1104choose viewing parameters step 1106 re-project morphed digital imagestep 1200 image 1202 length 1204 width 1300 source digital image file1302 image data 1304 meta-data 1306 aspect ratio

What is claimed is:
 1. A method for producing a cropped digital image,comprising the steps of: a) providing a plurality of partiallyoverlapping source digital images; b) providing a cropping aspect ratioL:H, the cropping aspect ratio being the ratio of the length to theheight of the cropped digital image; c) providing a cropping criterion,the cropping criterion being a criterion for the size and location ofthe cropped digital image; d) combining the source digital images toform a composite digital image; e) selecting the cropping region of thecomposite digital image according to the cropping criterion, saidcropping region being a rectangular region having aspect ratio L:H, andhaving size and location determined by the cropping criterion; and, f)cropping the composite digital image to the cropping region to form acropped digital image.
 2. The method claimed in claim 1, wherein thestep of providing source digital images further comprises the step ofdigitizing source photographic images to form source digital images. 3.The method claimed in claim 1, wherein the cropping criterion specifiesthat the cropped digital image is the composite digital image regionhaving a largest area out of the set of composite digital image regionshaving aspect ratio L:H.
 4. The method claimed in claim 1, wherein thecropping criterion specifies that the cropped digital image is thecomposite digital image region having largest area out of the set ofcomposite digital image regions having aspect ratio L:H that arecentered at the centroid of the composite digital image.
 5. The methodclaimed in claim 1, wherein the cropping criterion specifies that thecropped digital image is the composite digital image region havinglargest area out of the set of composite digital image regions havingaspect ratio L:H that are centered at the centroid of the main subjectof the composite digital image.
 6. The method claimed in claim 1,further comprising the step of: g) resizing the cropped digital imagefor display.
 7. The method claimed in claim 1, further comprising thestep of: g) resizing the cropped digital image for hardcopy output. 8.The method claimed in claim 1, further comprising the step of: g)transforming the pixel values of the cropped digital image to an outputdevice compatible color space.
 9. The method claimed in claim 1, whereinthe source digital images have pixel values that are linearly orlogarithmically related to scene intensity.
 10. The method claimed inclaim 9, wherein the step of providing source digital images furthercomprises applying a metric transform to a source digital image suchthat the pixel values of the source digital image are linearly orlogarithmically related to scene intensity.
 11. The method claimed inclaim 9, wherein the step of providing source digital images furthercomprises applying linear exposure transform(s) to one or more of thesource digital images to produce source digital images having pixelvalues that closely match in an overlapping region.
 12. The methodclaimed in claim 9, wherein the step of providing source digital imagesfurther comprises applying radial exposure transform(s) to one or moreof the source digital images to compensate for exposure falloff.
 13. Themethod claimed in claim 1, wherein the step of combining source digitalimages further comprises the steps of: i) warping the source digitalimages to compensate for distortion due to perspective projection,yielding warped digital images; ii) aligning the warped digital imagesto identify overlapping regions; and iii) blending the warped digitalimages in the overlapping regions to form a composite digital image. 14.The method claimed in claim 13, wherein the step of blending warpeddigital images includes calculating a weighted average of the pixelvalues in the overlapping region.
 15. The method claimed in claim 13,wherein the step of blending warped digital images further comprises thesteps of: i) projecting the warped digital images to simulate imagecapture on parallel image planes, forming projected digital images; ii)morphing the projected digital images in the overlapping regions to forma projected composite digital image; iii) choosing viewing parametersfor a composite digital image; and, iv) re-projecting the projectedcomposite digital image to simulate image capture with the chosenviewing parameters, forming a composite digital image.
 16. The methodclaimed in claim 1, wherein the step of combining source digital imagesfurther comprises warping the composite digital image to simulateprojection onto a geometrical surface suitable for viewing.
 17. Themethod claimed in claim 1, wherein the aspect ratio is a portrait aspectratio.
 18. The method claimed in claim 1, wherein the aspect ratio is alandscape aspect ratio.
 19. The method claimed in claim 1, wherein theaspect ratio is 3:2.
 20. The method claimed in claim 1, wherein theaspect ratio is 16:9.
 21. The method claimed in claim 1, wherein theaspect ratio is 3:1.
 22. The method claimed in claim 1, wherein theaspect ratio is 2:3.
 23. The method claimed in claim 1, wherein theaspect ratio is 9:16.
 24. The method claimed in claim 1, wherein theaspect ratio is 1:3.
 25. The method claimed in claim 1, wherein theaspect ratio is included as meta-data with at least one of the sourcedigital images.
 26. A system for producing a cropped digital image,comprising: a) a plurality of partially overlapping source digitalimages; b) means for specifying a cropping aspect ratio L:H, thecropping aspect ratio being the ratio of the length to the height of thecropped digital image; c) means for specifying a cropping criterion, thecropping criterion being a criterion for the size and location of thecropped digital image; d) means for combining the source digital imagesto form a composite digital image; e) means for selecting the croppingregion of the composite digital image according to the croppingcriterion, said cropping region being a rectangular region having aspectratio L:H, and having size and location determined by the croppingcriterion; and, f) means for cropping the composite digital image to thecropping region to form a cropped digital image.
 27. A computer programproduct for performing the method of claim 1.